The present invention relates to a high molecular weight epoxy resin which is characterized by containing highly pure bisphenol S substantially without bromine and which has a high glass transition temperature, and to an epoxy resinous composition containing the high molecular weight epoxy resin, an epoxy resin other than the high molecular weight epoxy resin and a curing agent as essential components. In particular, the invention relates to a resinous composition for a printed circuit board comprising the epoxy resinous composition.
Epoxy resins are used widely in paints, civil engineering adhesion and electrical uses, and, in particular, such resins as called phenoxy resins of BPA type having high molecular weights are used as base resins of varnish for paints and as base resins for filming, and also for adjustment of fluidity when added to epoxy resinous varnishes and for improvement in tenacity when cured. Those having bromine in its chemical structure are also used as flame retardants when blended with thermoplastic resins.
On the other hand, in the case of printed circuit boards used in electric and electronic devices, there are further required more multiple lamination, higher densification, thinning, lightening, high reliability and moldability with miniaturization, lightening and highly functioning of devices, in particular for multi-layered printed circuit boards. In reply to the requirements, there have been developed new methods for preparation of multi-layered printed circuit boards such as a buildup method. Therefore, there are required epoxy resins having high performances suitable for the methods.
As resins for multi-layered electric laminates, epoxy resins mainly having TBBA structure and containing bromine have been hitherto used. However, due to recent environmental problems, materials without halogen are being required. As counterplans therefor, there have been proposed uses of BPA type epoxy resins and multifunctional type epoxy resins. They are, however, not satisfactory in heat resistance, moldability or electrical characteristics. Thus, there has been desired an epoxy resin which satisfies these requirements and which does not substantially contain halogen.
Further, there are propositions to improve moldability or physical properties by adding BPA type high molecular weight epoxy resins or phenoxy resins. These are described, for example, in Japanese Patent Application Laid-open No. Hei 6-128461 and Japanese Patent Application Laid-open No. Hei 9-67555, but there is no description that bisphenol S type high molecular weight epoxy resins are used. Further, in Japanese Patent Application Laid-open No. Hei 5-295090, a bisphenol S type epoxy resin is described as one of difunctional epoxy resins that are raw materials of high molecular weight epoxy resins. There is, however, no description about purity and content of bisphenol S and, further, there is no description about characteristics as the bisphenol S containing high molecular weight epoxy resin.
In the case that a high molecular weight epoxy resin or phenoxy resin is added to a composition for a printed circuit board, moldability, flexibility, impact resistance and adhesiveness may be improved but heat resistance and insulating property become inferior when the composition is used to form the printed circuit board.
It is desirable to provide a high molecular weight epoxy resin containing highly pure bisphenol S without bromine, which is necessary for obtaining a composition for a printed circuit board superior in heat resistance, moldability, flexibility, impact resistance and adhesiveness, and also provides a resinous composition comprising the high molecular weight epoxy resin and a composition for a printed circuit board comprising the resinous composition.
There is now provided a high molecular weight epoxy resin obtained by polymerization reaction of a difunctional epoxy resin (X) with a dihydric phenol compound (Y) containing 70-100% by weight of bisphenol S in the presence of a catalyst, the high molecular weight epoxy resin being characterized in that a weight average molecular weight thereof is 10,000-200,000.
In one embodiment, there is also provided a high molecular weight epoxy resin as described above, characterized in that bisphenol S in the dihydric phenol compound (Y) contains 96% or more of 4,4xe2x80x2-bisphenol S.
In another embodiment, there is also provided a high molecular weight epoxy resin as described in any of the embodiments above, characterized in that the polymerization reaction is carried out at an equivalent ratio of [epoxy group in difunctional epoxy resin (X)]/[phenolic hydroxyl group in dihydric phenol compound (Y)]=1/0.94 to 1.06.
In yet another embodiment, there is also provided a high molecular weight epoxy resin as described in any of the embodiments above, characterized in that an epoxy equivalent of the high molecular weight epoxy resin is 5,000 g/eq. or more.
In a further embodiment, there is also provided a high molecular weight epoxy resin as described in any of the embodiments above, characterized in that a total content of Li, Na and K in the high molecular weight epoxy resin is 5 ppm or less, a content of nitrogen is 150 ppm or less and a content of phosphorus is 150 ppm or less.
There another embodiment, there is also provided a high molecular weight epoxy resin as described in any of the embodiments above, characterized in that the difunctional epoxy resin (X) is an epoxy resin obtained by condensation reaction of at least one selected from bisphenol A, bisphenol F, bisphenol S, 4,4xe2x80x2-biphenol and 3,3xe2x80x2,5,5xe2x80x2-tetramethyl-4,4xe2x80x2-biphenol with an epihalohydrin.
In another embodiment, there is also provided a high molecular weight epoxy resin as described in any one of items (1) to (6), characterized in that the difunctional epoxy resin (X) has a hydrolyzable chlorine concentration of 200 ppm or less and an xcex1-glycol group concentration of 100 meq/kg or less.
In yet another embodiment, there is provided an insulating resinous composition comprising the high molecular weight epoxy resin described in any one of the embodiments above, an epoxy resin other than the high molecular weight epoxy resin and a curing agent as essential components.
There is also provided a resinous composition for a printed circuit board comprising the high molecular weight epoxy resin described in any of the embodiments above, an epoxy resin other than the high molecular weight epoxy resin and a curing agent as essential components.